Conventionally, a fiberizing installation comprises a glass flow block, which receives molten glass coming from a feeder connected to the furnace in which the glass is melted, a bushing block and a bushing. The bushing is fitted at the bottom with a plate provided with a multitude of holes from which the molten glass flows, to be drawn into a multiplicity of filaments.
These filaments, the diameter of which may vary from 5 to 33 μm, are collected into at least one sheet that converges on an assembling device in order to form at least one strand, and, for example, to be wound up. Depending on its use, the strand may also be chopped, (to form chopped strands) or thrown onto a belt (to form continuous strand mats).
The products obtained are used mainly in various reinforcing applications.
The bushing is manufactured from an alloy of platinum and rhodium, which materials are electrically conducting and resistant over time to very high temperatures. This bushing is heated by Joule heating so as to maintain, at a certain temperature, around 1100 to 1400° C., the glass that it contains so that it remains in the molten state, so as to be drawn from the holes in the bottom of the bushing. The bushing is heated using an electrical transformer by the connection of two terminals, each located on each of the opposed sides of the bushing, to electrical connection elements external to the bushing.
The bushing terminals are attached by welding them to the side walls of the bushing. They project so as to be connected to the external connection elements.
These external connection elements are each in the form of a jaw clamp made of electrically conducting material, advantageously copper, which, by means of its two cheeks, clamps a bushing terminal, the jaw clamp being connected to a fixed busbar that is connected to the electrical transformer.
The jaw clamp is therefore a piece that is suspended after the connection terminal of the bushing and mechanically fastened by clamping it using a bolt passing through the cheeks of the jaw clamp.
The connection between the fixed busbar and the jaw clamp is itself provided by simple contact of a portion of the jaw clamp against the busbar, the latter being maintained at the desired height by any appropriate system for fastening onto a fixed element of the surroundings of the bushing, advantageously against the wall of the fiberizing booth.
The improvements made in recent years, such as the increased surface area of the bushing bottom, so as to have more filament-delivering holes, the cooling systems in the bottom of the bushing, and the mechanical reinforcement of the bushing have, on the one hand, created the need to be able to install in succession, in the same fiberizing position, bushings of different lengths and heights, and have, on the other hand, considerably increased the mass of the combination of the bushing and its peripheral equipment. Furthermore, the installing of these bulky bushings and this heavy equipment has made it more difficult for the various members to be accurately adjusted with respect to one another. Finally, the increased surface area of the bushing bottom and the increase in output from the bushing have meant that the electrical power delivered to the bushing in order to heat it has had to be increased. Consequently, the electrical conduction cross section of the jaw clamp had to be increased, which further increased the mass suspended beneath the bushing. The increase in size of these bushings has also resulted in a larger expansion of the bushing bottom, resulting in the generation of mechanical stresses in the terminals, in the bottom and in the actual body of the bushing.